Sensitivity of Different ACTH and Cortisol Concentration Values in Corticotropin-releasing Hormone-based Tests in Cushing`s Disease

Background:
Despite a set of multiple diagnostic tests, Cushing`s syndrome usually poses a diagnostic challenge.

Aim:
To determine sensitivity of several ACTH and cortisol concentration values in different time points in patients with Cushing`s disease (CD), during corticotropin-releasing hormone (CRH) stimulation test and during CRH stimulation following dexamethasone suppression (DEX-CRH) test.

Methods:
We retrospectively analyzed cortisol and ACTH concentration increment during CRH and DEX-CRH tests in 23 patients with confirmed CD. Cortisol and ACTH concentrations were determined immediately before, 15 minutes and 30 minutes after CRH stimulation. We evaluated the sensitivity of different cutoff values including those reported in previous studies, in the diagnosis of CD.

Results:
During DEX–CRH test, 15 minutes serum cortisol concentration of > 1.4 μg/dl (38 nmol/L) had a sensitivity of 90.9% for a diagnosis, and serum cortisol concentration ≥ 1.27 μg/dl (35 nmol/L) had a sensitivity of 100%. For plasma ACTH, sensitivity of 100% was obtained using ACTH ≥ 3.5 pmol/L (16 pg/ml) at 30 minutes.
During CRH test, 35% increase in ACTH concentration 15 minutes after stimulation had a sensitivity of 72.72% for a diagnosis. While, 20% increase in cortisol 30 minutes after stimulation yielded a sensitivity of 85.7%. The best sensitivity of ACTH and cortisol increment was obtained 15 minutes after stimulation, using 19% and 9% increase, respectively (sensitivity of 100% and 92.85%, respectively).

Conclusions:
During CRH and DEX-CRH tests, the study findings agree with the good sensitivity of ACTH and cortisol cutoff values suggested in previous studies; yet, other cutoff values may give a higher diagnostic sensitivity.